Concave head thumb screw



FIG. 1 is a top perspective view of a concave head thumb screw.

FIG. 2 is a bottom perspective view of the concave head thumb screw of FIG. 1 .

FIG. 3 is a side elevation view of the concave head thumb screw of FIG. 1 .

FIG. 4 is a bottom plan view of the concave head thumb screw of FIG. 1 ; and,

FIG. 5 is a top plan view of the concave head thumb screw of FIG. 1 . 

CLAIM The ornamental design for a concave head thumb screw, as shown and described. 